1. Technical Field
The present invention relates to a light source device and a projector.
2. Related Art
A projector known in the art includes a light source device, a light modulation device which modulates light emitted from the light source device to form image light corresponding to image information, and a projection lens which enlarges and projects the image light thus formed onto a screen or the like. A typical light source device included in this projector contains a discharge-type arc tube such as an extra-high pressure mercury lamp. According to this type of light source device, the temperature of the arc tube increases during light emission.
In this case, the temperature of the upper part of the arc tube easily rises, causing whitening of this part after continuation of the high temperature condition. On the other hand, an excessive low temperature of the lower part of the light emission portion causes blackening of the lower part. In either of these cases, the arc tube may lose its transparency. Therefore, sufficient cooling is required for the upper part of the arc tube to such an extent as not to excessively reduce the temperature of the lower part of the arc tube.
JP-A-2010-212186 discloses a technology which includes a housing accommodating an arc tube and a main reflection mirror. The housing has a hollow column-shaped body disposed on the front side of the main reflection mirror in the light emission direction in such a position as to surround the arc tube, and a duct member disposed on the outside surface of the column-shaped body as an air passage through which air flows in the circumferential direction of the column-shaped body. The top surface of the column-shaped body has an upper introduction port through which the air coming from the duct member goes into the column-shaped body. The upper introduction port is disposed in such a location that the center of the upper introduction port lies at a position shifted from the center axis of the arc tube toward the upstream side with respect to the flow direction of the air within the duct member when the column-shaped body is viewed from above. According to this structure, the flow passage of the duct member becomes shorter, and the resistance of the air flowing through the duct member decreases. Therefore, air having a sufficient flow speed and a sufficient flow amount can be securely introduced through the upper introduction port and supplied to the light emission portion.
According to the technology disclosed in JP-A-2010-212186, the arc tube is cooled by using air supplied only through the one upper introduction port. However, the recent improvement over the light emission efficiency of the arc tube (light emission portion) requires such a structure of the light source device which cools the arc tube with still higher efficiency. Therefore, development of a light source device and a projector capable of cooling the arc tube with excellent efficiency has been demanded.